The present invention relates to hydrofluorocarbons (HFC) based compositions as substitutes of CHClF2 (R 22). More particularly it relates to azeotropic compositions containing R 32 (difluoromethane, CH2F2) and ether of R 125 (CHF2xe2x80x94CF3) known as RE 125 (1,1,1,2,2-pentafluorodimethylether, CHF2xe2x80x94Oxe2x80x94CF3). Said compositions are very good working fluids for environmental air-conditioning plants and heat pumps.
R 22 is widely used as working fluid in room air-climatization. It is known, the R 22 being an HCFC, that it is subjected to production and use regulation and that therefore it will not be used any longer in the future.
The problem of the substitution of the CFCs as non dangerous refrigerants for the stratospheric ozone layer is well known. While for bringing to an end this substitution the HCFCs have been made available as transition fluids less dangerous than CFCs, their use is however regulated and this fact has caused many studies towards the definitive setting-up of new completely harmless fluids towards the stratospheric ozone layer. It is a characteristic of these latter fluids completely harmless towards the stratospheric ozone layer, not to contain chlorine atoms in their molecule and not to be usable in the area of the present equipments but to be usable in the area of the new ones or of the present equipments modified if necessary and working with different lubricants, for instance based on POE (polyols esters).
The substitution of R 22 with substitutes having the same characteristics, compatibility and performances has resulted among the most difficult ones among those up to now faced in the refrigeration field and it has not so far a viable solution.
In the case of the plants for home environmental air-conditioning and working by vapour compression cycles there is the possibility to use the same fluid both for cooling and for heating: this is possible with R 22. It is well known that by vapour compression cycle it is meant a refrigerating plant which takes advantage from the changes of physical state of the refrigerant which are finalized to remove heat from one side, during evaporation, and to release it to the other side, during condensation, thus obtaining a continuous heat transfer. The cycle is maintained at the expense of the required energy to compress the vapour.
The main characteristics of a working fluid in the mentioned application fields and generally in the whole field of the refrigeration and air-conditioning are well known:
easy to use,
reliability
chemical stability,
no toxicity,
suitable performances.
By suitable performances it is meant not only that the new fluid must be sufficiently effective from the point of view of the energetic consumptions and have a sufficient capacity of generating cool or releasing heat but also that, towards the fluid to be substituted, it does not require substantial modifications of the equipment design which must contain it and the change of the lubricating oil. Generally when a fluid has these characteristics it is called drop in.
By inertia and chemical stability it is meant that at the use pressures and temperatures alone or in the presence of lubricants and metals, air and moisture optionally absorbed, the refrigerant fluid does not undergo chemical degradation or variation of its performances.
The fluid even though it can be released in the environment because of small or great leaks of accidental type or of maintenance operations, being atoxic, guarantees the operator and final utilizer safety. By fluid compatible with the environment it is meant that it is completely inert towards the stratospheric ozone layer (ODP=0) and that it preferably has a small global warming power and any way lower than that it must replace (low GWP). By use easiness and reliability it is meant to refer to all those cases in which the fluid is not based on only one component but on more components. In all cases of multicomponent blends it is necessary to point out in which extent their characteristic may have influence during their handling and during their running in the plant. Indeed, depending on the chemical-physical properties of the fluid mixture, the storage, drawing, transfer and filling up phases of the refrigerating plant will be able to assure the nominal composition of the fluid in a more or less extended way. In other words some of the chemical-physical properties particularly affect the so called easy to use feature. By reliability it is meant a quite similar fact to this and which consists in assuring that during every kind of accidental or maintenance leak the fluid does not change its nominal composition and does not transform itself into compositions with different performances from the initial ones.
Easy to use feature and reliability of a refrigerant depend on the fact that among the chemical-physical properties of the refrigerant there is that to be an azeotrope.
By performances of a refrigerant fluid are meant known terms and especially two: COP (coefficient of performance) and Volumetric Capacity. By COP, which can indifferently be referred to a refrigerating cycle or heat pump, it is meant the energy given back from the fluid under the form of cold or heat with respect to that consumed in the compression. By Volumetric Capacity it is meant to indifferently refer to the cold or heat developed by volume unit of compressed fluid.
The need was felt to have available a refrigerant fluid having the combination of the above properties as substitute of R 22, in particular having the essential characteristic to be an azeotrope or near-azeotrope (as defined below), having COP and Volumetric Capacities similar or higher than R 22.
An object of the present invention is an azeotropic or near-azeotropic composition essentially consisting of:
35-99.1% by weight of CH2F2 (R 32), difluoromethane
0.1-65% by weight of CHF2xe2x80x94Oxe2x80x94CF3 (RE 125), 1,1,1,2,2,-pentafluorodimethylether.
In particular the azeotropic composition is the following:
90% by weight of CH2F2 (R 32), difluoromethane
10% by weight of RE 125, 1,1,1,2,2,-pentafluorodimethylether.
The compositions in the above range excluding the azeotrope are characterized in being near-azeotropic, i.e., after evaporation at constant temperature of 50% by weight of the initial mass of the liquid, the percent variation of the vapour pressure between the initial and final composition results to be lower than about 10%.
As well known an azeotrope is a specific mixture which has singular, unexpected and unforeseable chemical-physical properties, of which the most important ones are reported hereinafter. An azeotrope is a mixture of two or more fluids which has the same composition in the vapour and in the liquid phase, when it is in equilibrium under specific conditions. The azeotropic composition is defined by particular temperature and pressure values; under these conditions the mixtures undergo phase changes at constant composition and temperature as they were pure compounds.
A near-azeotropic blend is a mixture of two or more fluids which has a composition of the vapour substantially identical to that of the liquid and undergoes phase changes without substantially modifying its composition and temperature.
Generally in the prior art a composition is defined near-azeotropic as follows: after evaporation at constant temperature of 50% by weight of the liquid initial mass, the percent variation of the vapour pressure between that of the initial and that of the final composition results to be lower than about 10% as above described (to this purpose see the paper of D. A. Didion e D. B. Bivens in Int.J. Of Refrigeration, (vol.13, pag 163, 1990).
In the case of an azeotrope no variation of the vapour pressure between that of the original composition and that obtained after evaporation of the 50% of the liquid, is noted.
The azeotropic or near-azeotropic mixtures fall within the cases showing sufficiently positive or negative deviations from the Raoult""s law valid for ideally behaving systems.
Deviations with respect to the ideality are caused by unexpected and unforeseable intermolecular interactions among the components of the binary or ternary system such as to generate higher or lower interactions than those existing among the molecules of the pure products. When such deviations are sufficiently marked, the vapour pressure of the mixture in the azeotropic point is characterized by either lower or higher values than that of the pure components. Always for the azeotropic composition it is clear that, if the vapour pressure curve of the mixture shows a maximum, this corresponds to a minimum of the boiling temperature; viceversa to a minimum value of the vapour pressure it corresponds a maximum of the boiling temperature.
The azeotropic mixture admits only one composition for each value of the temperature and the pressure.
However, by changing temperature and pressure, several different azeotropic compositions starting from the same components can be obtained.
For instance the combination of all the compositions of the same components which have an absolute minimum or a maximum in the boilig temperature at different pressure levels form a range of compositions all azeotropic.
By boiling point at a certain pressure or bubble point it is meant, in the case of the mixtures of two or more components, the temperature at which the liquid mixture begins to form the first bubbles of its vapour. It is known in the art that such temperature can rise during isobar evaporation up to the moment in which the liquid is completely evaporated: this latter end boiling temperature is generally higher than the former and is defined dew-point. By boiling temperature it is meant the bubble point above defined. It has been surprisingly found that minimum azeotrope object of the present invention has refrigerating and heating performances better than average linear ones calculable from those of the pure components. The near-azeotropic compositions comprise the azeotropic one and have been shown by isobar measurements at p=1 atm (101 kPa). The azeotropic and near-azeotropic compositions of the invention have moreover a remarkable industrial interest since they unexpectedly show refrigerant capacity better than or similar to those of R 22, combined with COPs similar to those of R 22.
Furthermore it has been found that the compositions of the invention show a very good solubility at any temperature higher than xe2x88x9230xc2x0 C. with the polyol esters which are the most common alternative lubricants to hydrocarbon oils (mineral and synthetic) and to alkylbenzenes. This solubility feature is essential to assure the oil return to the compressor and avoid inconveniences in heat transfer due to oil accumulation in the evaporator. Besides, the compositions of the invention show to have the required characteristics as regards inertia and chemical compatibility in general. They indeed, once dissolved in POE and put into prolonged contact and at high temperature with the metals which usually are part of the air-conditioning unit, do not undergo chemical alteration nor cause chemical attack to the metals and neither generate chemical alteration to the lubricant in an extent higher than that caused by R 22 in the same conditions. This according to the ASHRAE 97-1983 (RA 89) method. In general the compositions with oil comprise a refrigerant fluid amount ranging from 35 to 99% by weight and oil from 1 to 65% by weight.
Among the near-azeotropic fluids, those having an R 32 content lower than 50% by weight are characterized by a vapour pressure similar to that of R 22 and by the non flammability.
It has been found that it is possible to add a third component to the binary compositions of the present invention without modifying the near-azeotropic behaviour. For instance R 125 or R 143a can be added in the following compositions:
R 32 35-95% by weight
RE 125 3-63% by weight
Third component 2-50% by weight.
In particular the following compositions:
R 32 35-50% by weight
RE 125 3-63% by weight
R 125 2-47% by weight
have resulted non flammable. This is an useful property in the case of leaks since the composition never becomes flammable.